Need selected radio button(HTML) values at server side

<input id="Radio1" type="radio" runat="server" name="rid"  />
  <input id="Radio2" type="radio" runat="server" name ="rid2"/>
  <asp:Button ID="Button2" runat="server" Text="Button" onclick="Button2_Click" />

protected void Button2_Click(object sender, EventArgs e)
{
    if (Radio1.Checked == true )
    {
        Response.Write("<script>alert('Checked')</script>");

    }
    else if(Radio2.Checked == true)
    {
        Response.Write("<script>alert('Checked 2')</script>");

    }
    else
    {
        Response.Write("<script>alert('not Checked ')</script>");
    }
}